Demands for nonvolatile memory devices provided with a rewritable nonvolatile memory, mainly for semiconductor memory cards, have been growing. Although the semiconductor memory card is very high-priced as compared to an optical disc, a tape media and the like demands for semiconductor memory cards as recording media for a mobile device such as a digital still camera, a mobile phone, or the like have been growing due to its advantages such as small size, light weight, shock resistance, convenience to handle, etc. This semiconductor memory card includes a flash memory as a nonvolatile main memory, and has a memory controller for controlling it. The memory controller performs a read-write control on the flash memory in accordance with read and write instructions from an access device in a main body of the digital still camera, personal computer, or the like. Moreover, there are not only some portable audio apparatuses using the semiconductor memory card as a memory device but also some portable audio apparatus installing a flash memory in the main body of the portable audio apparatuses. In recent years, the semiconductor memory card is not only used for consumer's application but also used in a professional moving image recorder in a broadcast station etc.
A flash memory installed in products such as the semiconductor memory card, portable audio apparatus, and the like requires relatively long time for writing and erasing to a memory array as a recording unit, and thus is so structured to be capable of collectively erasing and writing data to a plurality of memory cells. The memory card is composed of a plurality of physical blocks, each of which includes a plurality of pages. The erasing is performed in units of physical blocks, and the writing is performed in units of pages.
In response to demands for larger capacity and lower cost, predominating is flash memories, such as a multi-level NAND flash memory, of the type that are capable of storing information of two bits in one memory cell. Such a multi-level NAND flash memory has difficulties in ensuring the reliability of a memory cell and thus has a low guaranteed number of times of rewriting. The guaranteed number of rewriting is 100,000 for a conventional single-level NAND flash memory for example, but it decreases to one tenth, namely 10,000 for the multi-level NAND flash memory described above for example. Moreover, it also becomes difficult to manufacture a flash memory that can guarantee 10,000 times of rewriting.
The guaranteed number of times of rewriting in a flash memory is directly linked to the life of a semiconductor memory card and to the life of a device such as a portable audio apparatus itself. Conventionally, users who use the semiconductor memory card and an apparatus such as the portable audio apparatus have assumed the lives of these apparatuses to be semipermanent. However, when using a product loaded with the flash memory whose guaranteed number of times of rewriting is limited, it is important especially for users who frequently rewrite data to use it with consideration given to the life or to select a product while keeping the product life in mind.
To deal with this problem, as shown in Patent Documents 1 and 2 for example, a nonvolatile memory system which permits the user to recognize the life of a memory has been conventionally proposed. According to these documents, the user can recognize a rough life of the nonvolatile memory by displaying the rewriting number of times in a nonvolatile memory having a finite life to the user.
Patent Document 1: Japanese Unexamined Patent Publication No. Hei07-141899
Patent Document 2: Japanese Unexamined Patent Publication No. 2001-195316